1. Technical Field
The present invention relates to a measurement system for living bodies for measuring a response from a living body to a stimulus or instruction in order to obtain information about the living body.
2. Background Art
In a system for measuring a response from a living body to a given stimulus, the quality of a measurement signal can be expressed by an amplitude ratio of a response signal to other fluctuation components. The greater the amplitude ratio is, the higher the quality of the signal is. The fluctuation components are mainly fluctuations inherent in the living body (biological fluctuation components) and a noise inherent in the system. In order to improve the signal quality, according to a prior art technique, a stimulus (including a task instruction) is given repeatedly in a periodical or random manner, and the resultant response signal is calculated to obtain an arithmetic mean, as disclosed in an article A. Maki et al., Medical Physics 22, 1997-2005 (1995).
This conventional technique of giving a stimulus or instruction repeatedly in a periodical or random manner and then obtaining an arithmetic mean of the resultant signal is based on the assumption that the number of repetition is large. The random fluctuation components that appear in the arithmetic mean signal decrease in inverse proportion to the square root of the number of repetitions. However, the number of repetitions should be minimized, given the physical burden such repetitions place on the subject. Particularly, when the subject is an infant or a patient of certain diseases, it is impossible to repeat the measurement many times.